The present invention relates to recording and readback systems, and particularly those recorders which employ a specific code for recording data signals.
Digital signal recorders have been used in connection with data processing systems ever since the conception of data processing. Over the years, the recording density, i.e., the number of data bits recordable per unit of length, such as per centimeter, has been continually increasing. An advantage of increased data recording density is not only reduced access time to the data, but also the volumetric efficiency for storing data is enhanced. When data bit densities have passed 20,000 bits per centimeter, error rates increase to unacceptably high levels. At lower densities, exotic error correction codes are suitable for accommodating errors resulting from recording and readback of digital signals. Additionally, formatting of digital signals on a record medium includes interleaving, such that signals relatable to a given code word or set of code words are spaced along a record track. The effect of such spacing is to reduce the impact of signal dropouts, such as caused by debris on the medium; scratches, etc., on the medium; and momentary medium-to-transducer separation. While such interleaving is suitable for certain densities, at extremely high densities, i.e., at or above 20,000 bits per centimeter, interleaving to be effective for a suitable medium length becomes complicated and expensive to implement. Hence, other means must be provided to reduce the adverse effect of signal dropout while keeping the cost of such digital signal recorders to an acceptable level.
Another technique of increasing recording density is to increase the number of tracks per centimeter. As such tracks are placed closer and closer, unwanted signals from adjacent tracks can become a problem. Accordingly, it is desired that recording techniques be employed which reduce the effect of track-to-track signal transfer. Hence, noise immunity of the recording system should be inherent by the recording scheme and format of the signals on the record medium.